Recently, an IGCC (Integrated Gasification Combined Cycle) that includes a gasification unit and a combined power generation unit (combination of a gas turbine and a steam turbine) attracts attention. With the IGCC, heavy metals, sulfur, and the like included in raw materials such as residues and coal becoming as a fuel for a gas turbine are almost removed in the manufacturing process of a synthetic gas, which is used as a clean fuel gas equivalent to a natural gas. Consequently, since the environmental load can be reduced, IGCC is evaluated as environmentally friendly power plants for the next generation highly.
Generally, in such a type of system, the raw materials such as the residues and the coal are gasified in a gasification furnace, then harmful substances are removed therefrom to convert into a clean fuel gas in a gas treatment unit, and this fuel gas is used to generate power in a gas turbine.
In such a system, as the control method thereof, there is a gasification furnace lead control method in which the gasification furnace is controlled so as to produce a necessary amount of fuel gas corresponding to a request on the power generation unit, and the gas turbine is operated using this produced fuel gas. Moreover, there is a turbine lead control method in which a gas turbine is controlled so as to generate a necessary amount of power corresponding to a request of the power load, and a synthetic gas necessary for operating this gas turbine is supplied from the gasification furnace.
However, recently, a cooperative control method is adopted in which, in order to rapidly follow the variation of the power load request, the gasification furnace lead control method and the turbine lead control method are combined to perform a feed-forward control with respect to the gasification furnace.
Hereinafter, a description is given of the cooperative control method.
FIG. 3 is a circuit diagram illustrating a conventional IGCC. As shown in FIG. 3, the IGCC has a gasification process section 1 that gasifies fuels, and a combined power generation process section 2 that generates power by means of a gas turbine using the fuel gas supplied from the gasification process section 1.
A gasification process controller 5 to which a set value is sent from a gas pressure setting device 4 is connected to a fuel control valve 3 provided in the fuel feed line to the gasification process section 1. The fuel control valve 3 is controlled based on a control signal from the gasification process controller 5. The gasification process controller 5 calculates a control value from a measurement signal from a gas pressure instrument 6 that measures the gas pressure in the gasification process section 1 and the set value from the gas pressure setting device 4, and outputs a control signal to the fuel control valve 3.
Moreover, a power generation process controller 9 to which a set value is sent from a power load setting device 8 is connected to a gas control valve 7 provided in the gas feed line to the combined power generation process section 2. The gas control valve 7 is controlled based on a control signal from the power generation process controller 9. The power generation process controller 9 calculates a control value from a measurement signal from a power generation output measurement 10 that measures the power generation output in the combined power generation process section 2 and a set value from the power load setting device 8, and outputs a control signal to the gas control valve 7.
If the cooperative control method is performed in the above IGCC, a feed-forward compensator 11 is provided. The set value is sent from the power load setting device 8 to the feed-forward compensator 11. A feed-forward control signal is sent from the feed-forward compensator 11 to the fuel control valve 3. As a result, the feed rate of fuel that is supplied to the gasification process section 1 is increased or decreased depending upon the variation of the power load request.
That is, in this cooperative control method, it is possible for the gasification in the gasification furnace of the gasification process section 1 to rapidly follow the variation of the power load request.
As conventional technology documents of such a type of control, for example, there are Japanese Unexamined Patent Application, First Publication No. 2002-129910, Japanese Unexamined Patent Application, First Publication No. H 07-234701, Japanese Patent Publication No. 2685341, and Japanese Unexamined Patent Application, First Publication No. H 11-210412.
With an IGCC such as described above, it is necessary to stop the plant operation regularly, and to inspect the facilities. There is a case of shut down maintenance where the overall operation of the IGCC is stopped, and there is a case where, so as to enable stable supply of power, the combined power generation unit is continuously operated and only the gasification unit is stopped.
At this time, in the case of the IGCC having only one gasification unit, an auxiliary fuel such as kerosene is to be supplied to the power generation unit instead of the fuel gas produced in the gasification unit. When switching from the fuel gas to the auxiliary fuel, a highly advanced fuel change over technique is required in which the fuel is continuously changed over from the fuel gas produced in the gasification unit to the auxiliary fuel, while continuously operating the combined power generation unit. Conversely, there is a case where the auxiliary fuel is switched to the fuel gas, and a highly advanced fuel change over technique is similarly required.
In the above fuel change over, it is natural that the combined power generation unit has to be stably operated, that is, the power has to be stably and reliably supplied. At the same time, it is also required to stably operate without imposing an excessive impact on the gasification unit that supplies fuel gas to the combined power generation unit. Moreover, a demand for shortening the time required for this fuel change over operation is also a large factor from an economical viewpoint. Furthermore, making the fuel gas emission to the environment the minimum necessary is a required from the viewpoint of saving energy and minimizing the environmental load.